1. Field of the Invention
This invention relates to an improved pneumatically operated valve positioner and to a method of making the same.
2. Prior Art Statement
It was known to applicant to provide a vacuum operated valve positioner for positioning a valve member relative to a valve seat in relation to the magnitude of a pneumatic signal directed to the positioner.
It was also known to applicant that engine control systems for internal combustion engines have been provided wherein each has an exhaust gas recirculation valve for taking part of the exhaust gas of the internal combustion engine and diverting the same into the intake manifold to be again utilized in the internal combustion engine for polution control purposes. However, the degree of exhaust gas recirculation must be regulated according to various engine parameters, such as the RPM speed of the engine, the value of the manifold absolute pressure, etc., and it was suggested by others that it would be desirable to provide such a control system wherein the exhaust gas recirculation valve is pressure operated and pneumatically operated control means is provided for increasing a pressure signal from the engine air pump pressure supply to the valve as the engine RPM speed increases from a first value to a second value and for thereafter decreasing the pressure signal from the supply to the valve as the engine RPM speed further increases from the second value thereof to a third value, the control means producing the signal in substantially the same manner but at different values for different levels of vacuum at the manifold vacuum source thereof.
Thus, applicant previously invented such a control system and device as described and claimed in the copending patent application, Ser. No. 800,211, filed May 25, 1977, now U.S. Pat. No. 4,099,539, to control the operation of a pressure operated valve positioner as set forth in applicant's other copending patent application, Ser. No. 800,299, filed May 25, 1977, now U.S. Pat. No. 4,143,850.
However, it was subsequently suggested to applicant that it was desired to have such an exhaust gas recirculation valve be regulated only according to one engine parameter, namely, the value of the manifold absolute pressure and it was further suggested that manifold vacuum operate part of the valve positioner and that carburetor port vacuum operate another part of the valve positioner so that both parts would cooperate together to produce the desired operation.
Therefore, rather than use the above suggested two separate pneumatic sources, applicant invented a pneumatically operated valve positioner that operates only in response to one pneumatic signal source and which will function for the above purpose, such valve positioner using double diaphragms and being disclosed and claimed in the copending patent application, Ser. No. 908,209 filed May 22, 1978.
Another invention of applicant also provides a single signal valve positioner and such valve positioner utilizes a relay means in the actuator unit thereof and is disclosed and claimed in the copending patent application, Ser. No. 908,537, filed May 22, 1978.
Subsequently, it was suggested to applicant that it would be desirable to modify the double diaphragm valve positioner of above Ser. No. 908,209 so that a pressure signal from the engine air supply pump could be utilized to set the limits or values of operation of the valve positioner that is operated by the manifold absolute pressure.
Therefore, rather than modify the double diaphragm valve positioner of above Ser. No. 908,209, applicant has invented a pneumatically operated valve positioner of the relay type of above Ser. No. 908,537 to include means for having a signal from the engine pressure supply means set the values or limits of operation of the valve positioner that is operated by the engine manifold absolute pressure.